1. Technical Field
Aspects of the invention relate to a printing device which prints out print data including two or more objects by combining (stacking up) the objects while executing transparency processing for incorporating a transparent property (which can have been added to each object) into the combining of the objects, and in particular, to the speeding up and memory conservation of such a printing device executing the printing process including the transparency processing.
2. Related Art
A computer is capable of outputting data to various types of output devices such as printers. In recent years, an increasing amount of data described in PDLs (Page Description Languages), such as PDF (Portable Document Format® data, are being used, processed by computers, and outputted to printing devices.
The increasing use of PDLs comes from their device independence, that is, PDLs have the advantage of allowing the user to output data to output devices through a viewer operating on a computer independently of the OS (Operating System) installed in the computer. With this advantage, a document created with a PDL can be equally outputted from various computers as long as the computers are each equipped with a viewer. Similarly, a document created with a PDL can be equally printed out by various printers.
The PDL specifies the arrangement of characters, figures, etc. in each “page” which is handled as a target of display and printing. Such PDL data created with a PDL in many cases includes two or more objects (fonts, images, etc.) stacked up, in which an object overlaid on another object can have the transparent property. When an object having the transparent property is overlaid on another object, the color of the overlapping part (where both objects exist) varies depending on the degree of transparency which has been set to the upper object. Therefore, in order to output PDL data including such an overlapping part (where an upper object having the transparent property overlaps with a lower object), the so-called “transparency processing” has to be executed for the upper and lower objects.
The outline of the transparency processing is schematically shown in FIGS. 14 and 15. FIG. 14 is a conceptual diagram for explaining the printing of PDL data 60 including two objects. The PDL data 60 includes two objects: a first object A and a second object B which has the transparent property. When the second object B having the transparent property is drawn (overlaid) on the first object A, the overlapping part C is expressed with a color that is obtained by overlaying the color of the second object B (with the degree of transparency set to the second object B) on the color of the first object A. Thus, such an overlaying process (combining process) is realized by executing the transparency processing.
As a result, at the stage when the PDL data 60 is finally printed out, the two objects are printed on a print medium (e.g. paper) with the second object B (having the transparent property overlaid) on the first object A.
FIG. 15 is a conceptual diagram showing tasks executed in the transparency processing of PDL data. First, the PDL data 60 is stored in an intermediate data storage area 61 (reserved in a memory such as a RAM) as intermediate data. In this example, two pieces of intermediate data (first object A, second object B) are formed in the intermediate data storage area 61.
Subsequently, the transparency processing of the first and second objects A and B is executed in an area (called “transparency processing buffer 63”) reserved in the memory, separately for each of four layers corresponding to the four colors C (Cyan), M (Magenta), Y (Yellow) and K (blacK). In the transparency processing, the objects (data) in each layer are processed in many cases as 8-bit data for 256-step gradation.
Subsequently, the data obtained in the transparency processing buffer 63 is developed into a page memory area 64, and the developed image data is handed over to a print engine to be printed out. Since the page memory area 64 is required to be in a format that can be processed by the print engine, the data in each layer of the page memory area 64 is in many cases 2-step gradation data (having bit depth of 1 bit).
The details of the above methods are described in Japanese Patent Provisional Publication No. HEI 11-272252 (hereinafter referred to as a JP11-272252A), and Japanese Patent Provisional Publication No. HEI 11-286150 (hereinafter referred to as a JP11-286150A).
However, such conventional printing techniques have the disadvantage of slow printing speed in the printing of PDL data including a transparent object.
In the aforementioned example, the PDL data 60 including the second object B having the transparent property can not be directly developed into the page memory area 64; it is necessary to first execute the transparency processing to the PDL data 60 in the printer and thereafter develop the transparency-processed data into the page memory area 64. In short, a process like the one shown in FIG. 15 has to be executed in a printer.
Incidentally, PDL data 60 has to be processed in units of pages due to the nature of the data. However, the memory installed in an ordinary printer is generally designed considering the storing (reservation) of the page memory area 64 which is configured to have the 1-bit depth, and thus reserving areas for processing data having bit depth of 8 bits (intermediate data storage area 61, transparency processing buffer 63) requires a large free space in the memory. For example, just reserving the transparency processing buffer 63 requires a free space (per page) eight times that for the page memory area 64. For this reason, such a printer executing the transparency processing is required to be equipped with a memory of large storage capacity.
For the reason described above, the printing of PDL data including a transparent object needing the transparency processing can take an extremely long time when the printing process is executed by the CPU, the memory, etc. of an ordinary printer.
The printing speed can of course be increased by equipping a printer with a high-power CPU and a high-capacity memory to realize a higher data processing speed (throughput per unit time). However, the installation of such high-performance components in a printer is difficult since the CPU and the memory are especially expensive components which can drive up the manufacturing cost of the printer.
As explained above, the methods described in JP 11-272252A and JP 11-286150A involve the problems of slow printing speed in the printing of PDL data including a transparent object and high costs necessary for the implementation of high-speed printing of such PDL data.